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Grubs are the larvae of several different beetle species. Chafer beetles (Cyclocephala spp.), Japanese beetles (Popillia japonica) and May and June beetles (Phyllophaga spp.) are among the species that are considered grubs in their larval stages. The grubs are highly destructive to lawns. They feed on the roots of the grass in summer, resulting in dead patches of turf. Grub killers may be applied up to three times per year, depending on the pesticide and the manufacturer's instructions.

The Beetle Life Cycle

The majority of adult beetle species lay eggs in the summer. The grubs hatch and eat the grass roots until cold weather arrives. Then grubs burrow 2 to 8 inches into the soil to overwinter. When spring arrives and the soil warms, the grubs begin feeding on the grass roots again. In late spring and early summer, they pupate, and emerge as adults in midsummer.

Grub Damage

The grubs eat the roots of the grass, literally releasing the grass from the soil. Dead patches appear in spring when the grubs move back up to the grass and begin feeding. More patches appear in late summer and fall when the eggs hatch and new grubs begin their life cycle. Dig around the edges of the dead patches, and roll the turf away from the soil. The C-shaped grubs lie in the soil, under the dead grass. Depending on the species, these grayish-white grubs may be more than 1 inch long.

Preventative Grub Treatments

Preventative grub treatments should be applied either in spring to kill the overwintering grubs as they emerge from the soil, or in summer to kill the newly hatched grubs. Apply chlorantraniliprole products to the lawn in spring when the weather warms. Clothianidin, imidacloprid or thiamethoxam can be used in summer treatments to kill the new grubs as they emerge from their eggs and begin to feed.

Curative Grub Treatments

Carbaryl and trichlorfon kill grubs at all stages of their life cycle. The pesticides may be applied in spring or fall. When applied in early fall, they generally kill between 20 and 80 percent of the grubs. If you wait until late fall to apply the pesticides, they only kill 20 to 55 percent of the grubs. While the manufacturers' labels may indicate a speedy solution, curative treatments may take up to four weeks to take full effect on the grub population.

Pesticide Application

Mow the grass to remove flowering weeds and protect honeybees from the pesticides. Apply pesticide on a calm day when the forecast predicts clear weather for at least 24 hours. Put on a dust mask, safety goggles, rubber gloves, rubber boots, long pants and long sleeves before handling the pesticide. Set the spreader according to the label directions and fill it with the pesticide. Apply the granules evenly across the lawn. After applying the pesticide, water it into the lawn with at least 1/2 inch of water. Do not allow water to drain from the lawn into storm drains, gutters or waterways. Keep children and pets off the grass until it is completely dry.

Cultural Controls

While most grubs prefer a moist soil, some species of chafers prefer drier soils. If the lawn is infested by other beetle species, you can try keeping the grass dry in the summer. The beetle eggs will dry out and are likely to die. However, the grass will turn brown until you begin to water again. In general, keep the lawn healthy by maintaining the grass at the appropriate height for the species, deep watering weekly and fertilizing regularly.

About the Author

Ruth de Jauregui is an old-school graphic artist and writer who focuses primarily on garden topics. She writes a weekly garden column and authored 50 Fabulous Tomatoes for Your Garden. She continues to write nonfiction articles on gardening and other topics and is working on a second "50" book about plants that attract hummingbirds.